Accessibility Issue: Sortable table headers not read by sceen reader

[Michael-Hanley]

Describe the bug

• Table headers, when sortable, are not described by screen readers as sortable.
• When sorted, are not described by screen readers as sorted with their direction.
• When sort is changed, screen readers do not describe new sort configuration

To Reproduce

• Requires a screen reader such as NVDA

1. Go to a sortable example in the storybook
2. Click just above the table
3. Tab into headers
4. Headers will not be described as sortable

[AllenFang]

@Michael-Hanley thanks your PR, great job for this issue. I will release by this weekend. :)

[Michael-Hanley]

Awesome! Thank you!

[AllenFang]

https://react-bootstrap-table.github.io/react-bootstrap-table2/blog/2020/02/16/version-bump.html

upgrade to react-bootstrap-table-next to newest version